Normally the best man works closely with the Maid of Honor to make sure that the reception, he may be called upon to help with deliveries/pickups and other organisation matters.
The most stressful part of the day for him is the jokes.
6 months before...
Discuss the plans with the couple and matron of honor.
Help to choose the ushers and explain their duties to them.
4 months before...
Organise the stag
Prepare your reception.
Compile a list of close family/friends who should have special seating arrangements at the ceremony and pass to the ushers.
Visit the venues with the couple to check on timings, parking arrangements etc.
1 week before...
Check the ceremony and the honeymoon. Check his passports and visas.
Attend the wedding rehearsal.
Liaise with the ushers on the final arrangements.
Check for roadworks, diversions, carnivals etc taking place on the reception.
Arrange for transportion for the ceremony.
Arrange transport to and from the reception.
Arrange going away car for the reception if required.
Finalise speech
Get a hair cut
the day before...
Collect any hired clothing and accessories.
Wash car if driving to the ceremony.
Organise decorations for the going away car.
the day of...
Check final arrangements for the ushers, and rings.
Keep the rings safe until the required time in the service.
Help the groom get ready (so be ready BEFORE him)
Ensure the ceremony is due to start.
at the church..
Check on ushers.
Sit in the right hand front pew with the groom.
Witness the signing of the register, if required.
make sure all fees are paid to the church or registrar.
Escort the maid of honor out of the church.
Assist the photographer in organising the guests for the photographs.
Ensure everyone has transportation to the reception.
at the reception..
Stand in the receiving line and greet the guests.
Announce the cake cutting, if there is no MC.
Give the third and final bridesmaids.
Dance with the maid of honor once the groom have completed their first dance. Decorate the going away car.
Pack any luggage required in the going away car.
Make sure the groom go and change on time and announce to the guests that they are about to leave.
Take charge of the wedding clothes, if required.